The present invention relates to a sample heater for use in microscopes, and more particularly, to a heater which is capable of heating a sample positioned on a microscope sample supporter to a preset temperature.
A conventional sample heater for use in a microscope has been disclosed in Japanese Utility Model Publication No. Sho 57/1982-41774 published on Sept. 13, 1982, for example.
In a conventional heater, air of a predetermined temperature is fed into a heater box using a fan to heat or cool a container which contains a sample and its vicinity, whereby the sample is kept at the predetermined temperature.
The conventional heater has, however, the following disadvantages.
(1) Since air is fed into the heater box using a fan, there is a possibility that extraneous dust will be blown onto the sample and that dust within the box will stick to the sample. PA1 (2) When the heated air is fed into the heater box, an increased response time is required until the sample attains a predetermined temperature because of the low heat capacity of air. When the temperature of the sample is controlled in accordance with a time-program control an increased time is required for temperature stabilization. PA1 (3) When an open type culture observation container is employed, vapor steam evaporated from culture fluid within the container sticks to the inner surface of the heater box to cloud the inner surface. This degrades the ability to observe the sample.
In addition, the conventional heater has a temperature sensor disposed adjacent to the sample but away from it so as not to obstruct the view from the microscope. Therefore, a temperature controller controls the sample to a temperature based on an output signal from the temperature sensor and not from the sample itself.
However, when cultured cells are observed with a microscope, a culture observation container which is generally employed, for example, is so large in size in comparison with the culture that even when a temperature sensor is arranged in close vicinity to the container a significant temperature difference exists the actual temperature and the measured temperature. Positioning the temperature sensor within the container in the vicinity of the observation position may allow entry of various germs into the container through the temperature sensor so that every measurement requires cleaning and sterilization of the temperature sensor.
Some conventional sample heaters have an arrangement in which a heater plate is mounted on the microscope's sample supporter and a culture observation container is mounted on the heater plate to keep the sample within the container in a fixed temperature by the direct heat conduction from the heater plate.
In such sample heaters, since the heater plate is mounted on the sample support platform, or rest platform as it will be referred to herein, the sample is raised by thickness of the heater plate. In addition, a comparatively small diameter of a through-hole for the observation in the heater plate is chosen in order to improve the thermal insulation effect in the vicinity of the optical axis so that an allowable upward movement of an objective lens of an inverted type microscope is insufficient for the purpose of focusing. As a result, an out of focus condition may be caused and especially with an objective lens of the high magnification its operational range is generally so reduced that the front end of the objective lens hits against the heater plate, making it impossible to attain a required operational range. Thus, the microscope is limited to an objective lens of the small magnification. Furthermore, when a culture observation container such as a laboratory dish, flask and microtest plate is used, the sample is further raised by the bottom thickness of the container and thus the foregoing problem becomes more acute. When a non-inverted type microscope is used, the same problem is caused in connection with condenser lens.
Recently plastic laboratory dishes or flasks have been used. Such a plastic container generally has an annular projection on its bottom outer peripheral edge, which serves as a leg in the form of bottom rim to maintain the flatness of the bottom surface and to prevent the bottom from being damaged. Accordingly, when a sample within a culture observation container such as a laboratory dish or flask made of plastic is maintained at a fixed temperature by heating at least part of a rest for a microscope or a heater plate mounted on the rest so as to heat the observation container mounted on the rest or the heater plate by the heat conduction, only the projection is in contact with the rest and an air layer forms between the rest and the container bottom, so that uniform temperature is not obtained in the container. Thus, the sample within the container will not be heated properly. Also, the air layer produces a low thermal efficiency and an increased response time.